Continuation of ongoing work on the following projects: 1) Further biochemical and biological characterization of tissue-specific cell- aggregating factors. 2) The role of the cell surface in the control of DNA synthesis in embryonic neural cells, using lectins and other agents which specifically react with the cell surface. 3) Further analysis of glutamine synthetase induction in embryonic neural retina cells: (a) ontogeny of steroid receptors; (b) characterization of the receptors; (c) receptor associations with chromatin. 4) Studies on "pseudo- induction" of glutamine synthetase by certain inhabitors of macromolecular synthesis (Ara-C; proflavine). Bibliographic references: Hausman, R. E. and Moscona, A. A. Purification and characterization of the retina-specific cell- aggregating factor. Proc. Nat. Acad. Sci. US 72, 916-920 (1975). Sarkar, P. K. and Moscona, A. A. Nuclear binding of hydrocortisone- receptors in the embryonic chick retina and its relationship to glutamine synthetase induction. Am. Zool. 15(2), 241-247 (1975).